doc: improve wording of COPY commit 7ec73783d8

doc/src/sgml/ref/copy.sgml

@@ -489,9 +489,8 @@ COPY <replaceable class="parameter">count</replaceable>
 
    <para>
     <literal>FORCE_NULL</> and <literal>FORCE_NOT_NULL</> can be used
-    simultaneously on the same column. This has as result to convert quoted
-    null strings to null values and to convert unquoted null strings to
-    empty strings.
+    simultaneously on the same column. This results in converting quoted
+    empty strings to null values and unquoted empty strings to empty strings.
    </para>
 
  </refsect1>